The invention relates to appliances in general, and more particularly to electric appliances which consume water while in use. Typical examples of such appliances are steam irons, coffee, espresso and capuccino making machines and tea making machines. For the sake of simplicity and convenience, the invention will be described with reference to electric steam irons; however, it is to be understood that the invention can be embodied with similar or equal advantage in many other types of water-consuming appliances.
An electric steam iron normally comprises a housing which is provided with or carries an apertured sole plate and has a handle as well as a vessel for a supply of water. A steam chamber is provided in the housing to receive and confine steam which develops as a result of heating water to the boiling point and to supply steam to the apertures of the sole plate. The steam iron can be further provided with means for regulating the heating action and with means for regulating the rate of flow of water from the vessel into the range of the electric heating element or elements. As a rule, the vessel is filled with tap water which normally contains various gases as well as salts which are drawn from the soil or from the rocks with which the water comes in contact prior to entering a reservoir serving as a source of water for the taps in a dwelling or in another establishment. Salts which are customarily found in tap water include sodium bicarbonate, sodium sulfate and magnesium bicarbonate. The percentage of sodium and magnesium salts determines the hardness of water which is normally measured in degrees, such as the English or Clark degrees, the French degrees and the German degrees. The number of degrees is higher if the water is harder, and vice versa.
Hardness of water which is used in a steam iron exerts a great influence upon the useful life of the appliance. The reason is that heating entails a decomposition of water into its constituents, and such constituents, especially carbonates, deposit on the adjacent surfaces in the form of scale. The scale is an insulator of heat so that the energy requirements of the steam iron increase as the thickness of scale increases. In addition, scale gradually clogs various pipes, conduits and other components which define relatively narrow paths for the flow of water in the interior of a steam iron.
Heretofore known proposals to eliminate scale include the utilization of various acids. Thus, if the scale gathers on parts which are made of copper, brass or certain other metals, it can be removed with diluted lactic or acetic acid. The makers of steam irons recommend periodic descaling of such appliances; the length of intervals between successive descaling operations depends upon the hardness of water which is used in the steam irons.
It is further known to employ so-called decalcification or softness indicators in the form of electric or electronic instruments which contribute significantly to complexity and cost of the appliances. Moreover, presently known instruments of such character are not overly reliable which is another reason why they failed to gain widespread acceptance in the relevant industry.